Constant temperature molecular dynamics calculation on Lennard-Jones fluid and its application to water

Constant temperature molecular dynamics calculation has been carried out on Lennard-Jones liquid simulating argon. This method, proposed recently by Andersen, intends to transform the system from microcanonical to canonical ensemble and to keep the temperature of the system a constant value by the generation of random velocities when molecules exchange their energies with heat reservoir with a certain probability. A simple scheme is given for the estimation of collision probability and the effect of introducing this probability on dynamic behavior is examined in detail for 108 argon atoms as a test simulation. It is established that a collision probability of 0.01 is sufficient to realize the constancy of temperature reasonably well with no appreciable disturbance in the dynamic behavior. A model of pure water with Matsuoka-Clementi-Yoshimine (MCY) potential has also been simulated in the same manner. In the case of 2/16 MCY water at 298.15 K, the temperature difference is only 0.73 K with a collision probability of 0.005. Various static properties of MCY water have been calculated with reasonable agreement with those by previous Monte Carlo calculation, and moreover, the dynamic behavior calculated for MCY water gives a satisfactory picture on both translational and rotational motions in water, including reasonable agreement of diffusion coefficient with experimental datum.